CONSTITUTIVE EXPRESSION OF LYMPHOMA-ASSOCIATED NFKB-2 LYT-10 PROTEINSIS TUMORIGENIC IN MURINE FIBROBLASTS/

The NFKB-2 (Lyt-10) gene codes for an NF-kappa B-related transcription factor containing rel-polyG-ankyrin domains. Rearrangements of the NF KB-2 locus leading to the production of 3' truncated NFKB-2 proteins a re recurrently found in lymphoid neoplasms, particularly cutaneous lym phomas, Such mutant NFKB-2 proteins have lost the ability to repress t ranscription that is typical of NFKB-2 subunit p52, and function as co nstitutive transcriptional activators. To verify whether the expressio n of abnormal NFKB-2 proteins can lead to malignant transformations in mammalian cells, we transfected human lymphoblastoid cell lines and m urine fibroblasts (Balb/3T3) with expression vectors carrying the cDNA s coding far normal NFKB-2p52, Lyt-10C alpha or LB40 proteins, which a re representative of the abnormal types found in lymphoma cases. The e xpression of both normal and mutant NFKB-2 proteins has a lethal effec t on lymphoblastoid cells and a cytotoxic effect was also observed in murine fibroblasts. The fibroblast cell lines expressing Lyt-10C alpha or LB40, but not those expressing normal MFKB-2p52, were capable of f orming colonies in soft agar. The analysis of individual clones reveal ed that cloning efficiency correlated with the expression levels of th e abnormal proteins, Injection of the Lyt-10C alpha-transfected Balb c ells in SCID mice led to tumor formation in all of the animals, wherea s no tumors were observed in the mice injected with control or NFKB-2p 52-transfected cells, thus indicating that abnormal NFKB-2 protein exp ression is tumorigenic in vivo. Our results show that mutant NFKB-2 pr oteins can lead to the transformed phenotype, and support the hypothes is that alterations in NFKB-2 genes may play a role in lymphomagenesis .